Özet The purpose of the current study was to examine the relationship between elementary 8th grade students’ level of abstract thought in mathematics, their mathematical beliefs and their level of achievement in mathematics. The relational survey model, one of the quantitative research models, was employed in the study. The study group, formed through simple random sampling, was comprised of 527 8th grade students enrolled in a school in Hendek, Sakarya, during the 2012-2013 academic year. The data collection tools utilized in the study were the “Mathematics Belief Scale” and the “Mathematical Abstract Thought Test”. The statistical analyses conducted with the data obtained by means of these instruments yielded a positive relationship between students’ achievement scores and their mathematical beliefs and abstract thought levels, and between their abstract thought levels and mathematical beliefs. As a result, it was observed that the more positive students’ mathematical beliefs were, the more successful they were in mathematics, and the more positive their matematical beliefs were, the higher their abstract thought levels were.